Conventional fluid ejection systems, such as inkjet printing systems, include a printhead, an ink supply that provides liquid ink to the printhead, and an electronic controller that controls the printhead. The printhead ejects ink drops through multiple nozzles (also referred to as orifices) toward a print medium, such as a sheet of paper, thereby printing onto the print medium. Typically, the multiple nozzles are arranged in one or more arrays such that properly sequenced ejection of ink from the nozzles causes characters or other images to be printed on the print medium as the printhead and the print medium are moved relative to one another.
To enhance usability and simplify maintenance, certain fluid ejection devices incorporate one or more printhead assemblies, each including both a printhead and an ink supply. When the ink supply is depleted or if a different printhead is desired, the entire printhead assembly is replaced. A printhead assembly may be identified by an integrated programmable read-only memory (PROM). The PROM is programmed, during manufacturing or operations of the printhead, by blowing (also referred to as “burning”) one or more fuses contained in the PROM. Thus, each fuse in the PROM can carry one bit of information. Many different types of data can be programmed in a PROM. For example, a PROM can be programmed with a serial number, a model number, electrical calibration data, fluidic data, or other data.
One typical application of a PROM is to provide an identification number to a printhead assembly. To be unique, the identification number should be represented by as many bits as possible. Although a PROM is an effective means of providing such an identification number, the size of the identification number that can be programmed into the PROM is limited to the number of fuses multiplied by one bit per fuse (i.e., either the fuse is intact or completely blown).
Thus, there is a need to increase the amount of information provided by a PROM circuit without increasing either the cost or complexity of the PROM circuit.